This invention relates to an electron gun and more particularly to an electron gun of a type having a thermionic source of electrons disposed on a head, an accelerating electrode, and a platform to support and position the head relative to the accelerating electrode.
Electron beam furnaces are used to heat materials to produce vapors for deposition on an article. An electron beam furnace includes an electron gun, a deflection system, and a cooling system. The electron gun generates an electron bean. The deflection system directs the electron beam toward the material to be heated. The cooling system cools the electron gun to prevent it from overheating.
The electron gun typically includes an electron source, a focusing electrode, and an accelerating electrode. The electron source is typically a cathode heated by an electric current to cause the cathode to emit electrons. The focusing electrode is typically negatively charged to repel the electrons and thereby direct the electrons in a direction generally toward the accelerating electrode. The accelerating electrode is positioned downstream from the electron source and the focusing electrode. The accelerating electrode is typically less negatively charged than the electron source and the focusing electrode to cause the electrons to form into a beam and travel in the downstream direction.
In one known type of electron gun, the electron source and the focusing electrode are elongated and disposed in a head. The head is supported by a platform spaced apart from the accelerating electrode. This type of electron gun is reliable and available in many different power ratings. The physical size of the head, the accelerating electrode, and the platform of a given one of these electron guns depends on its power rating.
It is important that an electron gun to be used in an electron beam furnace generate an electron beam suitable for the type of material to be heated and the type of deposition sought for the article. Different types of materials and depositions require electron beams of different amounts of electron beam power and may require different electron beam shape. However, it is desirable to have electron beam guns operate in a space charge limited mode. In such mode, the above described type of electron guns generally perform best at a power equal to or slightly below its power rating. Consequently, no one of these electron guns can adequately generate electron beams for all of the electron beam powers required.
Whenever an electron gun in the electron beam furnace does not generate an electron beam suitable for the type of material to be heated and the type of deposition sought for the article, the traditional approach has been to remove the electron gun and replace it with an electron gun that provides a suitable electron beam. However completely replacing an electron gun can be difficult and time consuming. Moreover, the deflection system and the cooling system of the electron beam furnace are connected to the accelerating electrode of the electron gun and are designed to suit the physical size of the accelerating electrode and the power rating of the electron gun. Consequently, replacing the electron gun requires replacing the deflection system and the cooling system, thereby compounding effort involved.
An object of the present invention is to reduce the effort involved with providing an electron gun of the above described type to generate a suitable electron beam for a particular type of material and deposition.
The present invention is predicated in part on the recognition that the accelerating electrode of a first electron gun having a first power rating can be operated with a head from a second electron gun having a second power rating substantially different than the first power rating, to provide an electron beam comparable to that which would be provided by the second electron gun, and that such operation is facilitated by making the platform adjustable enough to be able to support and position the head of the second electron gun, which may be physically smaller than the head of the first electron gun.
According to a first aspect of the present invention, a method includes providing an electron gun having an accelerating electrode and a first head with a thermionic electron source, and further includes replacing the first head with a second head having a power rating substantially different than that of the first head, and subsequently operating the electron gun without replacing the accelerating electrode.
This method reduces the effort associated with providing an electron gun that generates an electron beam suitable for a particular type of material and deposition. As used herein substantially different means that one of the heads is at least twenty five percent less than the other of the heads. Using this method, suitable electron beams of various power levels can be generated by replacing the head of an electron gun without the need to replacing the accelerating electrode of the electron gun, thereby saving time. In one detailed embodiment, the power rating of the second head is at least twenty five percent less than the power rating of the first head. In another detailed embodiment, the accelerating electrode is connected to a deflection system and a cooling system, at least one of the deflection system and the cooling system is not replaced prior to operating the electron gun with the second head, thereby reducing the difficulty and the amount of time consumed.
According to a second aspect of the present invention, an apparatus for an electron gun has a head having a thermionic electron source and at least one reference member, an accelerating electrode, and a platform spaced apart from the accelerating electrode and having at least one locating member that engages the at least one reference member of the head to position the head in three dimensions relative to the accelerating electrode, wherein the at least one locating member is adjustably located and the location of the at least one locating member can be adjusted by at least nine millimeters (mm).
Such apparatus is useful in practicing the above described method, but is not limited to such. In order to operate the accelerating electrode of the first electron gun with the head of the second electron gun, it is desirable to be able to support and position the head on the platform of the first electron gun. However, as described above, the head of the second electron gun may be smaller in size than the head of the first electron gun. Providing the platform with locating members that are adjustably located by at least nine mm enables the platform to support and position heads of various sizes.
As described hereinbelow, although adjustably located locating members are known, until now, their adjustability was limited to less than five mm, being merely intended to compensate for manufacturing tolerances of components of the electron gun and to facilitate alignment of the electron source and the accelerating electrode.
According to a third aspect of the present invention, an apparatus for an electron gun has a head having a thermionic electron source, an accelerating electrode, and a platform that supports the head and is adjustably spaced from the accelerating electrode.
This apparatus enables the shape of the electron beam to be varied by varying the distance between the electron source and the accelerating electrode. The apparatus is useful in practicing the above described method, but is not limited to such.
These and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description, accompanying drawings, and claims.